Mechanical circulatory support devices have gained increasingly common use in end stage heart failure patients. Presently, more than a thousand patients per year are treated with implantable ventricular assist devices (VADs), as bridge to transplant, bridge to recovery, or for permanent use. The pusher plate and other types of positive displacement pumps approved by the FDA are large, heavy, and generally noisy devices which have major limitations, including poor reliability and a high incidence of serious adverse events such as bleeding, infection, thromboembolism, and stroke. Over the past five years, rotary blood pumps have been undergoing clinical trials in the United States, or have received CE mark approval for use abroad. The Jarvik 2000 intraventricular axial flow pump VAD, has been used in over 100 patients, and has supported a patient almost five years, longer than any other single VAD of any type. One patient has survived for over 6 years with the old type positive displacement pump, but only after his original implant device wore out and it was replaced with a new one.
Although rotary blood pumps of many designs represent a very promising improvement over the old generation positive displacement VADs, none has yet reduced the incidence of serious adverse events to a practically negligible rate. Published data indicates that the three month mortality with all types of VADs remains at approximately 20-30%, a rate which is only acceptable in patients facing the risk of imminent death at the time of surgery. Many experts in the field recognize that early mortality is increased if the VAD is not used until the last minute, when the patient's deterioration is advanced. Earlier application of the less invasive rotary blood pumps holds promise to reduce early mortality, but no device developed to date has been recognized by surgeons, cardiologists, and the public as a true “breakthrough device” appropriate to implant in NYHA class III patients, who have serious heart failure but are not yet facing a risk of imminent death.
No heart assist device is better than its worst characteristic. If everything were perfect except the durability were less than two years the device would have limited usefulness for permanent implantation. If it were durable for decades but had a very high incidence of serious infection, it would find limited use. If it had excellent long term freedom from failure and no serious adverse events, but required highly invasive surgery, with high surgical mortality and prolonged post implant hospitalization, it would not be widely accepted.
Experience teaches that each and every level of device complexity brings potential problems, and ultimate simplification is the best approach to solve all limiting problems. Experience also teaches that despite the greatest care to prevent damage to external components, such as batteries, cables, and connectors, and despite concerted efforts to educate patients and caregivers in proper daily use, damage, mistakes, and oversights can never be completely avoided. Therefore, the safest VAD is one which is designed to permit it to be safely turned off for at least enough time to replace external components with backup equipment.
Regarding complexity, almost all VADS have significant problems associated with the inflow and outflow conduits used to connect the devices to the circulatory system. The Jarvik 2000 avoids the need for any inflow cannula, because the pump is placed directly inside the ventricle. But it still requires an outflow graft which must be sutured to the aorta and has been the site of bleeding complications. The present invention eliminates both the inflow cannula and the outflow graft. Only one other type of device does this, a pump placed within the outflow valve orifice, disclosed by Yozu in U.S. Pat. No. 4,994,017, and further described in scientific publications such as “The valvo-pump, an axial blood pump implanted at the heart valve position: concept and initial results.” 1: Artif Organs. 1992 June; 16(3):297-9. Despite elimination of the inlet and outlet cannulae, pump placement within the entire valve orifice, as disclosed in the prior art, has significant disadvantages. If the pump stops, the patient's natural heart has no valved outlet, and therefore it cannot pump effectively to support the patient even for a short time. If an axial pump with a large cross sectional flow area is used, there will be massive aortic regurgitation and the natural heart will fail. If an axial pump with a small cross sectional flow area is used, there may be little regurgitation, but there will be high resistance and the natural heart will not be able to eject sufficient blood.
In the present invention, the axial flow pump is only placed in one third of the valve area, and the other two thirds of the area is a functional valved outflow channel. The axial flow pump may be designed with a small cross sectional flow area, in which case regurgitation will be minor, and the natural heart will pump effectively.
The degree of miniaturization made possible by the present invention is dramatic compared both to the “old model” pusher plate pumps such as the HeartMate or Novacor, and even compared to the smallest rotary blood pumps in clinical trials, i.e. the Jarvik 2000, the MicroMed DeBakey VAD, and the HeartMate II, which are all more than ten times the size and weight of the transvalvular device disclosed herewithin.
The preferred embodiment of transvalvular pump of the present invention displaces only 2.5 cc of volume and weighs only 8 grams. At 1,800 grams the Novacor weighs 225 times as much. At 1,200 grams, the HeartMate weighs 150 times as much. At 340 grams the HeartMate II weighs 42 times as much. At 112 grams the Micromed VAD weighs 14 times as much, and at 85 grams the Jarvik 2000 weighs 10 times as much. At 25 cc the Jarvik 2000 is the smallest permanent VAD in clinical use, and it is still ten times as large as the transvalvular device of the present invention.
This degree of miniaturization far surpasses any known permanently implantable heart assist device in the prior art, and enables minimally invasive surgical techniques that are not otherwise possible.
Other inventions disclosed in the prior art utilize small axial flow pumps placed beyond the aortic valve with the valve left in place, such as Nash, U.S. Pat. No. 4,919,647, “Aortically located blood pumping catheter and method of use” and Pasque, U.S. Pat. No. 5,290,227, “Method of implanting blood pump in ascending aorta or main pulmonary artery”. If these pumps stop, the aortic valve will still function, so the natural heart can sustain the patient. However, by placing the pump above the openings to the coronary arteries, the pressure in the coronary arteries is reduced to intraventricular pressure during diastole (˜5 mmHg), which is detrimental to coronary artery flow, rather aortic diastolic pressure (˜70 mmHg), which is necessary to provide normal coronary artery flow.
One basic distinguishing characteristic of the present invention compared to some prior art inventions using axial pumps at the aortic position or just distal to it, is that the pump is placed in parallel with the natural heart rather than in series as in Yozu, Nash, and Pasque.
Another prior art approach using miniature axial flow pumps near the aortic valve is disclosed by Barbut in U.S. Pat. No. 6,136,025, “Endoscopic arterial pumps for treatment of cardiac insufficiency and venous pumps for right-sided cardiac support”. The pump may be placed across the aortic valve, with a balloon surrounding it to occlude the aorta, effectively producing a series configuration. If no balloon is used, the pump may lie in a cannula across the aortic valve and function in parallel, similar to the arrangement with the Wampler in U.S. Pat. No. 4,625,712 “High-capacity intravascular blood pump utilizing percutaneous access”, Jarvik in U.S. Pat. No. 5,888,241 “Cannula pumps for temporary cardiac support and methods of their application and use”, and by Rau in U.S. Pat. No. 6,176,848 “Intravascular blood pump”. However, in any pump where a cylindrical cannula is passed through the central portion of the aortic valve and the leaflets must seal against the cannula, the shape of the valve leaflets does not exactly match the cannula. Also, there is motion of the cannula relative to the valve. These factors make the valve leaflets subject to erosion if the cannula is left in place long term. In the present invention, the device is designed with non-cylindrical facets that properly match the configuration of the closed valve leaflets to avoid erosion, and the pump is fixed in position relative to the leaflets. The faceted surfaces upon which the tissue valve leaflets seal may be covered with natural tissue, such as a portion of the natural valve leaflet of the patient or treated pericardium, to minimize erosion to the functioning valve leaftets. In another embodiment, a mechanical heart valve and miniature blood pump are combined and implanted at the aortic annulus. The mechanical valve may use one or more rigid pivoting leaflets, flexing polymer leaflets, or a confined mechanical occluder such as a valve ball.